I've got a site where users can post their goods for sale. When posting, they can choose multiple, predefined categories.
Problem I'm trying to solve here, how to present this large list of categories, in a clean, attractive and easy to use manner?
Right now, I'm using the ToCheckList jQuery plugin to make a checklist.
Maybe the best pattern would be a format people are more familiar with like a multiselect list (I can't remember its "official name")
Another pattern to consider would be using categorized list in either a selection tree or accordion ( sorry I couldn't find any examples of this).
You could organize your categories into subcategories, then use a Live Filter to allow users to drill down to the available options that they'd like to select.
One technique I've used previously (with mixed success) for an internal app was browser keyboard shortcuts on each checkbox. No clicking, just Alt-B, Alt-X.
I'm a fan of tagging - you could go for an interface similar to tag interfaces in various stack-engine sites (stackoverlow.com, doctpye, superuser.com). It's a search-as-you-type box that brings up tag options below. Easy to use, easy to store.